1. Field of the Invention
The present invention relates generally to bicycles and more particularly, to a pneumatic and hydraulic elevating seat tube assembly of a bicycle.
2. Description of the Related Art
The conventional pneumatic and hydraulic elevating seat is worked by means of the compressibility of gas and the flowing of hydraulic oil in a space, which changes the relative position between an outer tube and a seat post, so that the height of the seat is adjustable.
In the related prior art, such as Taiwan Patent No. M406117, a main body of a piston is provided respectively on internal and external surfaces thereof with two annular grooves which are opened in opposite directions and overlap each other, and two sealing members are disposed in the two annular grooves respectively, so that the gas and the hydraulic oil are isolated from each other by the two sealing members staggered with each other. However, in the above-mentioned patent, because the two sealing members should be arranged at the inside and the outside of the piston, the main body of the piston has a disadvantage of having a too large external radius. For matching the external radius of the main body of the piston, the size of the outer tube is difficultly reduced and therefore may be affect the spatial arrangement of other elements.